The present invention generally relates to gas generation systems and particularly to systems and methods for on-board inert gas generation with a turbocompressor, used to inert fuel tank ullage space of aircraft.
As the fuel level is reduced within aircraft fuel tanks, the ullage space that develops in the fuel tank contains potentially combustible combinations of oxygen and fuel vapors in dangerous proximity to a variety of possible ignition sources. The conditions present within the ullage space change during the course of a flight and depending on the temperature, pressure and fuel type, a catastrophic explosion may result. Limiting the oxygen content within the ullage space of a fuel tank significantly helps to immunize a fuel tank from explosions. Industry standards have suggested various limits for the oxygen content of gaseous fill in the ullage space of a fuel tank. For example, current standards suggest that the minimum amount of oxygen needed to sustain combustion at sea level is slightly less than 12%. That amount increases to 14.5% at 30,000 feet above sea level.
Attempts have been made to reduce the oxygen level in aircraft fuel tanks by providing fuel tank foam systems to arrest explosions. Foam inerting systems typically require initially displacing approximately 3.5% of the volume of the tank, reducing the amount of fuel that can be carried by the aircraft. Maintenance requires periodic removal of the foam, a task that involves significant dismantling and down-time Nitrogen-generating systems (NGS) have been used to inert the ullage space by introducing nitrogen enriched air into the fuel tanks, significantly reducing the amount of oxygen present. Typically, an NGS passes compressed air from the engines through filters to separate out the nitrogen content, which is then piped into aircraft fuel tanks.
An on-board inert gas generation system typically involves a sequence of thermal and pressure variations of gases moving through the aircraft and eventually expelled by the aircraft into ambient temperatures and pressures. In high-altitude and fast-moving aircraft, small variations of temperature and pressure created by the expulsions can introduce forces that may disrupt the efficient flight performance of the aircraft.
As can be seen, an on-board inert gas system that produces required quantities of inert gas while minimizing potentially disruptive exhaust conditions is needed.